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JAKE TAPPER, CNN ANCHOR: Game on. The biggest event of the election year is just hours away, and it's right here on CNN.

A special edition of THE LEAD begins right now.

Good afternoon, everyone. Welcome to a special edition of THE LEAD, debate night in America.

I'm Jake Tapper, live at Hofstra University in Hempstead, Long Island, New York, where tonight Donald Trump and Hillary Clinton will for the first time ever be on the stage for the first presidential debate, the biggest event of an unpredictable and unprecedented election year with what could be the biggest debate audience in the history of the world.

An estimated 100 million people could be tuning in, and it all gets under way at 9:00 p.m. Eastern right here on CNN. The race is either candidate's at this point, with national polls tight and key battleground states up in the air.

And tonight it comes down to 90 minutes broken into six 15-minute segments with no commercial breaks. Right now, you're looking at the debate stage. Clinton will be at the shorter podium you see on your right. Trump will be on your left. A coin toss decided who goes first. Team Clinton won that. She get two minutes to answer the first question, and then Trump will get the same question, same two.

The audience in the hall will be forewarned, no applause, no cheering. We will see how that holds. This is Long Island.

Clinton has been prepping for this debate for weeks, and especially these last few days, working late into the night at a hotel near her Chappaqua home, we're told, even going through one last practice session as recently as this afternoon.

Donald Trump also spent part of today prepping with aides. For a candidate whose primary debate performances have included references literally below the belt, political observers wonder how unchained he will be.

Our correspondents are covering every angle of this historical debate.

We will begin with Sara Murray in the spin room here on the Hofstra University campus.

Sara, how did Mr. Trump spend the day?

SARA MURRAY, CNN NATIONAL POLITICAL CORRESPONDENT: Well, Jake, even though Donald Trump's campaign has tried to play this expectations game, they have tried to highlight the amount of debate prep Hillary Clinton has been doing, and sort of downplay the way Trump is doing his, he did sneak in another last-minute debate prep session today.

Reince Priebus, the RNC chairman, was with him for that. And other people that he's had around for these are really folks that he sees as peers, people like Chris Christie, people like Rudy Giuliani, people who don't just have experience in the political arena, but also have policy experience and can help Donald Trump on the substance of this, as well as the tone.

And he really comes into tonight with two key challenges. One of them is to show that he can talk about complicated issues beyond the generalities, that he can dive into details, into political specifics, into his policy prescription on a lot of these questions.

But of course the other is the temperament issue. We have seen a lot of voters who are turned off by Hillary Clinton, but they're also turned off by Donald Trump. That's particularly important in the suburbs. It's particularly important with female voters.

So we're going to be looking to see whether we do see a more gracious Donald Trump on stage, whether we see someone who wants to appear presidential and will debate Hillary Clinton on facts, on sort of her record, rather than some of those below-the-belt references you mentioned earlier, Jake.

TAPPER: All right, Sara Murray.

Let's go now to Jeff Zeleny. He's been covering the Clinton campaign.

Jeff, what are you learning about how Secretary Clinton is spending these last few hours?

JEFF ZELENY, CNN SENIOR WASHINGTON CORRESPONDENT: Well, Jake, Secretary Clinton has driven here to Long Island from her home in Chappaqua after really going through several mock debate sessions.

She has made no apologies for the fact that she is indeed preparing for this debate in an old-fashioned setting. For the past several evenings, at the exact pointed hour of the debate, 9:00 p.m. Eastern time, she has stood on a mock stage in a hotel near her home and they have gone through this debate.

She is doing it with a stand-in for Donald Trump, a stand-in for the moderator and a small group of advisers. But, Jake, this afternoon, she is resting, she is reading, and she is getting ready for what is surely the biggest night of her campaign here.

Yes, we have seen her on the debate stage so many times, about 38 or 39, by my count, going all the way back to 2000. This is a different moment entirely. She realizes that. Her campaign realizes that, particularly given the polls in Colorado, in Pennsylvania, our new battleground polls there, as well as nationally.

What she's trying to do, I'm told, Jake, is make her case, is make her argument for why voters should be more liking her. Donald Trump is already, you know, somewhat a known factor in this, and her opposition to him is known.

[16:05:00]

But she's going to be making a positive case for herself, as well as fact-checking when she can. I'm told by her advisers she does not want to be -- they do not want her to be the constant fact-checker throughout the course of the whole evening.

But she surely will on some cases, and taking Donald Trump's words to him. If he shows up as a more disciplined candidate tonight, I'm told, she will remind voters, remind that big audience of some of the things he has said throughout the course of this long campaign -- Jake.

TAPPER: All right, Jeff Zeleny, thanks so much.

Neither Trump nor Clinton has ever before participated in a general election debate, of course. Clinton has not debated a Republican in a decade, since her Senate reelection contest in 2006. And while she and Bernie Sanders squared off five times mano a mano in the Democratic primaries, Trump, for his part, even though he participated in 11 Republican debates, he has never gone one on one against any rival.

Sunlen Serfaty is live outside the debate hall.

Sunlen, how was it decided who is speaking first? By a coin toss?

SUNLEN SERFATY, CNN NATIONAL CORRESPONDENT: That's right. This was decided by a coin toss, so we will first hear from Hillary Clinton tonight, Jake.

She will get the first question fielded to her. She will have two minutes to answer that. That same question then goes over to Donald Trump for two minutes. And then that will open up this sort of open question-and-answer, open debate session, where they will have a discussion for 10 minutes.

And this 90-minute debate will largely follow this same format where they have six segments, exactly like that, 15 minutes of debate, centered around each a specific topic, foreign policy, economy, national security.

There will be no commercial breaks during that 90 minutes, no bathroom breaks, no chance for the candidates to huddle quietly with any aides for a few quick moments.

They're also, interestingly enough, tonight will not be any sort of buzzer to indicate when the candidates inevitably go over their allotted time. That tonight, Jake, is the sole responsibility of the moderator, Lester Holt.

TAPPER: All right, Sunlen Serfaty, thank you so much.

Joining me now to talk about the debate is Clinton campaign manager Robby Mook.

Robby, thanks so much for being here. Appreciate it.

First of all, let me get your response to CNN's battleground polls showing that it's a very, very tight race, within the margin of error, in two states you really need to win, Pennsylvania and Colorado. I don't think your campaign is even on the air in Colorado and hasn't been in weeks. Was that a mistake? Do you need to put TV ads back on there?

ROBBY MOOK, HILLARY CLINTON CAMPAIGN MANAGER: Well, Jake, you're absolutely right. These are both important states to that math, to 270 electoral votes.

Our internal numbers show something a lot steadier and in some cases very different than what a lot of these public polls show. The public polls have kind of bounced around.

TAPPER: Both in Pennsylvania and Colorado?

MOOK: In both states, we have seen all kinds of different outcomes.

But, look, operationally, we know what we need to do. We're running like we're 20 points behind. We're going to put everything we have into both of these states to turn our supporters out. We're going to make decisions about television as we go along. But I feel really confident in the strategy we have, which is, we're all in.

TAPPER: We're about five hours away from the start of the debate. Clinton is here on Long Island right now. We're told that she's relaxing, she's reading.

She obviously is somebody -- I don't think anybody would say she's unprepared when it comes to the issues. She didn't really need to bone up on the briefing books.

So what has she been working on? Has she been working on how to prepare for insults from Donald Trump, how to fact-check without falling into the trap that many say Al Gore fell into kind of seeming arrogant, in a way, in the 2000 debates? What has been the biggest lesson that she has trying to learn in terms of the performance of this?

MOOK: Well, at every point in this campaign, she has done best when she has the opportunity to present directly to the voters the plan she has to make a real difference in their lives, and not just as president, but that this is -- this campaign is really a lifelong mission for her, to fight for kids and families, to make that difference.

So that's key. But, look, what we're asking for in this debate -- you know this very well -- we want these candidates to be judged fairly. Do they both have specific plans to make people's lives better? Do they both have a real command of the issues?

Donald Trump has not demonstrated that so far. And, lastly, Donald Trump can't lie and win this debate. You can't get a passing grade with the kind of just factual errors that he puts out whenever he speaks.

TAPPER: How much are you expecting Lester Holt to fact-check? Because I think the Commission on Presidential Debates has made it clear that they don't think that the primary role of the moderator is to say, pardon me, candidate X, but that's not true, here are the facts, one, two, three.

MOOK: Well, look, this is his call to make. He's in charge, and we respect that.

But I think there is a role for the moderator just to call it out quickly if someone is saying something that's patently untrue. The problem is, Donald Trump has such a penchant for telling these lies.

If Hillary Clinton had to fact-check him herself every time, she won't have time to say her own thing, to tell people what she wants to do for them to make a difference as president.

So, we think it's only fair that there be a little bit of fact- checking. Let's not let Donald Trump get away with this. But, most importantly, you can't get a passing grade when you lie, and you can't get a passing grade when you don't have a command of the issues.

[16:10:03]

TAPPER: Donald Trump on the campaign stage, on the trail, has been critical of Hillary Clinton when it comes to her behavior relating to Bill Clinton's infidelities, a subject I wouldn't bring up, except that he brought it up over the weekend when he talked about Gennifer Flowers possibly being invited, which the campaign says now they're not going to do that.

In fact, he has accused Hillary Clinton of going after some of the women that have been Bill Clinton's accusers. Is she ready for that? Have you guys mocked -- have you gamed out any possible question from Donald Trump, because really it's -- the sky is the limit. You have watched the debates.

MOOK: Well, I think the truth is on our side here, and so are the voters.

First of all, no one has fought more for women's rights than Hillary Clinton for her entire career. So, she's happy to have that debate any time. But, furthermore, is this really what Donald Trump wants to make this debate about?

TAPPER: I don't know. He brought it up over the weekend, which is the only reason I bring it up now.

MOOK: And that's his choice. And that's his choice.

But what the voters want are real plans from these candidates about how they will help them afford college, how they will help them get the health care they need at an affordable price, bring down the cost of prescription drugs, how they will keep this country safe. That's what the voters want to hear about.

That's what Hillary Clinton is here to talk about. If Donald Trump wants to drag this down, that's his choice, but I think the voters will judge that pretty harshly.

Obviously, both candidates have talked about bringing guests that could get in the other's head. I think, in all fairness, you guys started it with the Mark Cuban invitation, the billionaire who has been a critic of Trump. Do you think that can work? Might Hillary Clinton go out, see Mark Geist, and that rattles her, or no?

MOOK: Look, what is going to Hillary Clinton a fantastic president is her steadiness and her strength.

She's not going to get rattled by this sort of thing. And, look, I would make a distinction. Mark Cuban is a business leader. He's someone that came off the sidelines into politics because he is concerned about Donald Trump's temperament.

And as a business leader, he thinks Hillary Clinton is going to do more to create jobs and raise wages in this country. That's very different than some of the controversial figures like Gennifer flowers that Donald Trump has talked about.

And I think it's that lack of seriousness that is bringing people like Mark Cuban to Hillary Clinton.

TAPPER: All right, Robby Mook, thanks so much for being here. We appreciate it.

DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: First of all, this guy is a choke artist, this guy is a liar.

(CROSSTALK)

TRUMP: You're the basket case.

(END VIDEO CLIP)

TAPPER: Plus, whose job is it to fact-check the candidates this evening?

And one of the biggest challenges of debating Hillary Clinton has nothing to do with policy.

(BEGIN VIDEO CLIP, 2000)

RICK LAZIO (R), NEW YORK SENATORIAL CANDIDATE: Right here. Sign it right now.

HILLARY RODHAM CLINTON (D), NEW YORK SENATORIAL CANDIDATE: Well, we will shake on this.

LAZIO: No, no, I want your signature.

(END VIDEO CLIP)

TAPPER: Will Trump fall into what many perceive to be a trap?

This special edition of THE LEAD, stay with us.

(COMMERCIAL BREAK)

[16:16:54] JAKE TAPPER, CNN ANCHOR: Welcome back to a special edition of THE LEAD. Debate night in America.

Just hours from now, Hillary Clinton and Donald Trump will take the stage here at Hofstra University on Long Island for the first presidential debate, an incredibly important night in a crucial decision for the nation. New polls show the candidates neck and neck in Colorado and Pennsylvania, two states critical to either's chances of becoming the next president.

Dana Bash joins me now.

And, Dana, Clinton has a slight edge in the polls, but it's much narrower than a month ago. Her post-convention bounce has mostly vanished. And Trump really has momentum. The numbers are going in his direction. If he passes the test tonight, her campaign, I'm sure, is very worried.

DANA BASH, CNN CHIEF POLITICAL CORRESPONDENT: Absolutely. There's no question about. Even though their public bravado is quite different, those two polls that we have out today are exhibits A and A-plus in those two states that shouldn't be battleground states for her that are.

And just to kind of give you an example of the kind of information that we're hearing from the Clinton campaign ahead of tonight's debate, I was told by a source familiar with the prep that Philippe Reines, who is Clinton's long time aide, former aide now, who is playing the role of Donald Trump in their mock debates, that a few days ago he shifted from an opening statement with Trump bombast to Trump as a polite combatant, talking about the fact she will be the first woman nominee and deserves congratulations for the glass ceilings she has broken. So, Philippe Reines has been playing the Donald Trump. Now, Jake, you and I have been around this for a long time. When we get nuggets like that, our question is, why are we being told this, and my answer is they actually believe Donald Trump could come out and be polite, and they don't want people -- they kind of want to lead up to the moment with getting people used to that idea so people aren't surprised, and then they say, oh, wow, look at Donald Trump, it's a different Donald Trump.

That is the kind of psychological warfare that we have been dealing with and will continue to deal with into tonight and, of course, after tonight is over -- Jake.

TAPPER: That, of course, would depend on Donald Trump and his team watching cable news which, of course, we know they don't.

Dana Bash, thank you so much.

Joining me now, our panel of CNN political analysts and contributors. We have with us, former presidential adviser for Presidents Nixon, Ford, Reagan and Clinton, only four presidents? David Gergen. Senior writer for "The Federalist", Mary Katharine Ham, presidential historian Douglas Brinkley, "USA Today" columnist Kirsten Powers, Donald Trump supporter Jeffrey Lord from the beautiful city of Harrisburg, former mayor of Philadelphia and Hillary Clinton supporter, Michael Nutter, CNN's national political reporter Maeve Reston, and presidential historian Tim Naftali.

Thanks one and all for being here.

David Gergen, the Clinton campaign getting prepared, making sure everybody knows they're prepared for nice Trump, for restrained Trump. Would you tell Mr. Trump if you were advising him that that's actually the good play for him, to be the restrained, nice Mr. Trump?

[16:20:03] DAVID GERGEN, CNN SENIOR POLITICAL ANALYST: Jake, I think he'd tell him to dial it back some, but don't dial it down to docile, you know? Don't dial it down to boring. He's got to be himself.

You want the candidate to be himself to bring out the best qualities, and he has to be authentic. And Donald Trump, I think he'll be very polite in the beginning but I would imagine the fireworks will start within 10 minutes or so.

TAPPER: And, Jeffrey, this is the Trump we saw during the primary debates.

(BEGIN VIDEO CLIPS)

DONALD TRUMP (R), PRESIDENTIAL NOMINEE: First of all, this guy is a choke artist and this guy is a liar. You're a basket case.

This little guy has lied so much about my record.

First of all, Rand Paul shouldn't be even on this stage.

Excuse me, one second. (CROSSTALK)

More energy tonight, I like that.

He referred to my hands as small. Something else must be small. I guarantee there's no problem, I guarantee you.

(END VIDEO CLIPS)

TAPPER: Certainly one for the history books. Do you expect that Donald Trump tonight? He calls her crooked Hillary when he's out on the stump. He certainly doesn't hold back.

JEFFREY LORD, CNN POLITICAL COMMENTATOR: I do expect some version of it in the sense that he will use it to make a point. If he's talking about the Clinton Foundation, he will, I suspect, go down that path. If he's talking about other things, he may do some version of that.

I mean, I think David is right. I mean, there has to be a balance here. He has to ratchet back a little bit, but he is going to be Donald Trump. Make no mistake about that.

TAPPER: What are you expecting today, Mr. Mayor?

MICHAEL NUTTER (D), FORMER PHILADELPHIA MAYOR: I think we should expect the usual schizophrenic Jekyll and Hyde kind of Donald Trump. The person has no ability to constrain contain or restrain himself. Vacuous on policy, and we'll just have five-word sentences without a noun or a verb.

MAEVE RESTON, CNN NATIONAL POLITICAL REPORTER: Wow. How do you follow that?

TAPPER: I'm not sure who the mayor is voting for, but -- Maeve, what are you expecting? You've covered Donald Trump for this whole contest. Are you expecting him to be as, shall we say, colorful as we saw in those clips?

RESTON: No, certainly not. I do think that, you know, as much as they have downplayed the prep that he's been doing, he has been thinking seriously about the answers he wants to formulate. A very different kind of debate prep than what Hillary Clinton is doing.

But I think in some ways she has the harder task tonight. You know, she's got a really fine line to walk in terms of the balance between fact checking and keeping him in his place and seeming likeable. You know, reaching out to all of his millennial voters who she needs help with in Colorado and Pennsylvania. So, it's going to be really fascinating to watch.

TAPPER: Mary Katharine, let me go to you, because obviously we know not everybody watches the entire debate. Usually the first half hour is better rated than the last half hour. For the beginning, what are you expecting from Donald Trump and what are you expecting from Hillary Clinton? MARY KATHARINE, CNN POLITICAL COMMENTATOR: I think he can probably

come out and be calm in a more reined-in, Kellyanne Conway style of Donald Trump. I don't know how long that will last. But if people -- if it happens at the end of the debate, it will also make it onto the Internet so people will be aware of it, but I think in the beginning you can count on him being pretty chill.

I know the Clinton followers are like how is it so deeply unfair that his expectations are so slow that that it doesn't seem like he has to do that much to beat her, and she has to do all this over here? Welcome to the world of Marco Rubio and the rest of the guys who stood on that stage. He hasn't done this before, and his expectations are lower for that reason.

TAPPER: But is that fair, Kirsten?

KIRSTEN POWERS, CNN POLITICAL ANALYST: No, I don't think it's fair. But you also have to remember that the Clinton campaign has also told everybody that there's basically a madman is out there and that's who is expected to show up on the stage. If he shows up and he doesn't look like a madman, then he has -- he's won at least that tiny little thing.

But I think that -- you have to remember, he's a showman, so the chances of him spending the entire time being boring are very low because he understands what people want is a showman. So he has to figure out how to be interesting but ado that he's on stage with a woman, which is different in a primary with what he was doing in the primaries. If he tries to do that with Hillary, it might not work as well.

TAPPER: I'd like to build a wall right here, the people chanting.

Professor Brinkley, let me show you something, because one of the things that's interesting is that this is obviously the first time there's been a female major party nominee on that stage. Let's take a look at some of the missteps the pundits have said previous Hillary Clinton opponents have made.

(BEGIN VIDEO CLIP)

HILLARY CLINTON (D), PRESIDENTIAL CANDIDATE: Well, I would be happy to when you give me the signed letters --

UNIDENTIFIED MALE: Right here. Right here. Sign it right now.

CLINTON: We'll shake -- we'll shake on this, Rick.

UNIDENTIFIED MALE: No, I want your signature because I think everybody wants to see you signing something that you said you're for.

JOHN EDWARDS (D), FORMER U.S. SENATOR: I admire what Senator Clinton has done for America, what her husband did for America. I'm not sure about that coat.

TAPPER: To be fair to the John Edwards clip there, he was asked to name something he didn't like about one of his opponents. But it is a challenge, the gender dynamics.

DOUGLAS BRINKLEY, CNN PRESIDENTIAL HISTORIAN: Absolutely. Hillary Clinton is going to take what LBJ did to Barry Goldwater.

[16:25:02] The slogan of LBJ in '64 was, in your gut, you know he's nuts. She wants to have people see Donald Trump is being nuts, nuts about climate change, what he's denied, nuts about talking about women's health, nuts about race.

How do you do that? Well, she is politically correct. She's a trained creature of politically correctness. She's getting hammered for being politically correct, but there's damage that can be done if you're not politically incorrect at all. And I think that's a pitfall for Donald Trump. She's going to try to lure him in to some these debates to get him to say something that's gauche and deeply unappealing.

TAPPER: Tim, what do you think? What are you looking for this evening?

TIM NAFTALI, CNN PRESIDENTIAL HISTORIAN: Donald Trump is a very competitive man. I think his behavior will depend on whether he thinks he's winning this debate or not. If he thinks he's losing this debate, I think you'll see the other Trump.

The other thing that's important is the dynamics of the crowd. The crowd isn't supposed to say anything, unlike this crowd, right? He always says his worst things not at the beginning, it's never his topic sentence, it's reiteration when he wants more from the audience. If he doesn't get that tonight, it may be easier for him to be restrained. But I look for him to get very competitive. If he doesn't think he's winning, he doesn't want a draw.

TAPPER: Very interesting.

Stay with us all.

Next, countdown to the debate. We are awaiting the candidates' arrivals here at Hofstra University.

Plus, it's one of the hardest things about debating Hillary Clinton. We'll explain. You're watching a specialist edition of THE LEAD. Stay with us.